1. Field of the Invention
The present invention relates to a cloned single-stranded DNA comprising a nucleotide sequence which encodes an antibacterial polypeptide precursor, a cloned double-stranded DNA consisting of the single-stranded DNA and its complementary single-stranded DNA, a DNA fragment of the single- or double-stranded DNA, a process for the preparation thereof, and a plasmid, in which the double-strand DNA or its fragment is inserted.
2. Related Arts
It has been known that a certain antibacterial substance will appear in a body fluid, when a vaccine is inoculated to an invertebrate such as insecta ["Eur. J. Biochem." Vol. 106, page 7, (1980)].
One of the present inventors has found that the flesh fly (Sarcophaga peregrina) produces a certain antibacterial polypeptide in its body fluid, when a larva of the insect is injured in its body wall, the polypeptide being separated and purified to investigate its physicochemical properties [see Jap. Pat. Nos. 59-13730 (A) published Jan. 24, 1984 and 61-122299 (A) published June 10, 1986].
Further, the inventor has found several antibacterial polypeptides from culture supernatant of a cell line (named as--NIH-Sape-4--) established from Sarcophaga peregrina embryo, one of the polypeptides being purified to investigate its physicochemical properties and structure and to find that the polypeptide consists of 40 amino acids with 6 cysteine residues in its molecular structure (Jap. Pat. Appln. Nos. 14806/1987 and 14807/1987 which correspond to U.S. Pat. Appln. Ser. Nos. 146,893 and 146,892 as well as European Pat. Appln. Nos. 88100799.1 and 88100801.5, respectively).
Since each of the antibacterial polypeptides produced by the insect of Sarcophaga peregrina or obtained through cultivation of the cell line shows a relatively wide antibacterial spectrum, almost no toxicity and is one of proteins, the substance has been expected as one of edible antibiotics and also expected as one of anti-tumour or anti-virus substance, but a process for preparing the polypeptides has a problem that a shift of its, laboratorical production to industrial mass-production accompanies remarkable difficulty.